MACHINING TIMING BELT PULLEYS

[Brian Rupnow]

Okay, people, today we're going to take a look at making timing belt pulleys. Small timing belt pulleys are absolutely the cat's meow for the things I run with my model engines. The images seen in this post are downloaded cad models of the pulley I used on my overhead cam engine two years ago.

[Brian Rupnow]

This is the engine. Not a great picture of the engine, but a good picture of the timing belt pulley.

[Brian Rupnow]

Here we have the cad model of the same pulley. and we see that a 0.118" (3mm) rod fits exactly into one of the spaces between the teeth.

[Brian Rupnow]

Here we have the same cad model with two 3 mm diameter rods laid side by side in the pulley grooves. The measured angle between them is purely a resultant, and will change with the number of teeth in a given pulley diameter. It is interesting that the dashed "pitch line" runs exactly through the center of the 3 mm diameter rods. The diameter of this pitch line is 2.407", or 61.14 mm.

[Dan Rowe]

Brian, what is the belt series or name? Did you drill holes or use a milling cutter like cutting a gear?

Cheers Dan

[Brian Rupnow]

This gets easier for me if I pull it onto a drawing sheet. It is apparent that the outside diameter of the gear is .054" (1.37 mm] greater than the pitch diameter. If we break that down into radius differential, then it is .027" or 0.686mm.

[Brian Rupnow]

Dan, I didn't do either. I purchased the gear. I'm trying to figure out how to make a cutter so I can make one. The part number for this pulley is  A6A25-040NF091---Brian.

[Dave Otto]

Dan, I didn't do either. I purchased the gear. I'm trying to figure out how to make a cutter so I can make one. The part number for this pulley is  A6A25-040NF091---Brian.

3mm ball end mill?

[Roger B]

Interesting  These pulleys are obviously based on some concept. Reverse engineering it might be fun 

[Brian Rupnow]

If I wanted to make a single tooth cutter with a 1.5 mm tip radius and make many, many passes to cut each space between the teeth I could make one as shown (with some relief ground on the tip) .

[Jasonb]

The two external corners of the "U" should be rounded so you need more than a half round cutter, think they are usually hobbed or the cheap ones extruded.

https://gear.com.my/wp-content/uploads/pdf/page55.pdf

[Brian Rupnow]

Or--I could take a piece of 3 mm thick 01 steel bar, and first cut it like this---

[Brian Rupnow]

And then drill some holes like this---

[crueby]

Ah, the old drill-holes-then-turn-off-the-rim-trick, eh?!   (read in your best Get-Smart voice)

[Brian Rupnow]

And then go in and cut the material away between the holes, I might end up with something like this.  This is the part that becomes a real challenge. I'm good with drilling the holes as shown in the previous step, but I think that removing the material between the holes to end up with this would be beyond what I can do. After this step I would still have to profile both sides to end up with a 1.5 mm radius on the end of the points, then harden and heat soak the part.